1. Field of the Invention
The present invention relates to a door closer, and more particularly to such a door closer, which comprises a double-threaded adjustment rod controlled to regulate the spring power of the compression springs of the reciprocating mechanism thereof in adjusting the return speed of the door.
2. Description of the Prior Art
A regular door closer comprises an air cylinder fixedly fastened to the doorframe, and a reciprocating rod moved in and out of the air cylinder and fixedly connected to the door. This structure of door closer is functional, however the air pressure of the air cylinder is not adjustable. When installed, the user cannot adjust the return speed of the door.
The invention has been accomplished to provide a door closer, which eliminates the aforesaid drawback. According to one aspect of the present invention, the door closer comprises a casing, the casing comprising a hydraulic cylinder holding a hydraulic fluid, two tunnels disposed in communication with the hydraulic fluid in the hydraulic cylinder, and two end cap means respectively fastened to the tunnels at one end remote from the hydraulic cylinder; a coupling block mounted in one end of the hydraulic cylinder, the coupling block comprising a pivot shaft adapted for fastening to a door; and a reciprocating mechanism coupled to the coupling block and to move the pivot shaft in closing the door being fastened to the pivot shaft. According to another aspect of the present invention, the casing further comprises a plurality of mounting hole spaced between and disposed in communication with the tunnels, and a plurality of fluid velocity regulating valve respectively installed in the mounting holes and secured in place by a respective washer. According to still another aspect of the present invention, the adjustment rod comprises a plurality of O-rings respectively disposed in contact with an inside wall of the casing, the O-rings including a first O-ring disposed adjacent to the outer end of the adjustment rod to stop the hydraulic fluid from leaking out of the casing, and at least one second O-ring respectively disposed between each two of the mounting holes for enabling the fluid velocity regulating valves to work independently.